Currently almost half of all trauma mortality is directly or indirectly attributable to hemorrhagic shock, accounting for more than 50,000 deaths yearly in the U.S. and hundreds of billions of dollars in economic costs. Active Signal Technologies proposes to develop an Acoustic Resuscitation Monitor (ARM) for enabling non-invasive assessment of systemic perfusion in real time, with the ultimate goal of developing a device that can continuously monitor shock and resuscitation in the field. As no such device exists and current perfusion tests have significant lag time, ARM can significantly improve patient outcome and lower costs both for in-hospital (Phase I) and field (Phase II) settings. The ARM technology is based on Active Signal's Brain Acoustic Monitor (BAM) - demonstrated effectively in brain perfusion studies on more than 500 trauma and 100 stroke patients. In Phase I Active Signal with the University of Maryland Shock Trauma Center will conduct feasibility tests on approximately 100 patients with 5 data collection times. Specific aims are to determine the relationship between vasoconstriction as indicated by ARM using pulse-waveform characteristics and systemic perfusion measured by current clinical metrics, and to reconfigure the BAM to monitor vasoconstriction at 3 arterial tree levels.